Worship is basically an act of giving honor and glory to God for who He is or what He has done, for all of His and Its worth. However, not all acts of worship is really worship. I myself have been guilty of false worship at times.
One, my guilt of being a hypocrite worshipper. It is the greatest punishment of all that I have experienced. Whenever I know that deep inside me I am rebellious against God or that I willingly sin, then my conscience will really go hard against me. Worse is the pain that the Holy Spirit gives me as He is grieved. But those pains, especially the one coming from the Holy Spirit is for my good working towards my repentance.
Matthew 15:8 (KJV) This people draweth nigh unto me with their mouth, and honoureth me with their lips; but their heart is far from me.
Second, coming to worship knowing that someone has something against me. With my relationship with others destroyed, I really find it hard to worship God. In fact, it is impossible.
Matthew 5:23-24 (KJV) Therefore if thou bring thy gift to the altar, and there rememberest that thy brother hath ought against thee;
Leave there thy gift before the altar, and go thy way; first be reconciled to thy brother, and then come and offer thy gift.
God demands holiness in His children, especially during times of sacred worship, individually or as a Church. Worship is a blessed act of reverent adoration to the God whose Holiness is in a class of its own. Therefore, worshipping Him with unclean hearts and hands is not acceptable.